This invention relates to a method of applying coating solutions on support materials (hereinafter referred to as "a web", when applicable) in the manufacture of photographing photo-sensitive materials such as photographic papers, photographic materials for printing such as lithographic film and printing plate, and recording materials such as pressure-sensitive recording sheets and heat-sensitive recording sheets. More particularly, this invention relates to a method of multi-layer coating at least two coating liquids to a moving web.
One example of a high speed coating method for a slide hopper-type coating apparatus according to a multi-layer coating of this type has been disclosed in U.S. Pat. No. 4,001,024. In this method, the wet coverage of the lowermost layer is in the range from about 2 to about 12 cubic centimeters of coating composition per square meter of web surface and the lowermost layer is formed from a coating composition with a viscosity in the range from about 1 to about 8 centipoises, and the vortical action of the coating bead is confined within the lowermost layer and the layer immediately above it, whereby interlayer mixing occurs between the lowermost layer and the layer immediately above it but all other layers are coated in distinct layer relationship.
In U.S. Pat. No. 4,113,903, a coating method is disclosed in which the layer next to the web a shear thinning carrier layer of pseudoplastic liquid having a viscosity between 20 and 200 centipoises at a shear rate of 100 sec.sup.-1 and a viscosity below 10 centipoises at a shear rate of 100,000 sec.sup.-1. That is, in this method, the lowermost layer is formed of a pseudoplastic solution having a high viscosity with a low rate of shear and a low viscosity with a high rate of shear, in order to eliminate the instability of the bead in the U.S. Pat. No. 4,001,024.
In the above-described coating method, the coating solution forming the lowermost layer shows a non-Newtonian fluidity. Therefore, the coating solution must be prepared by using special compounds.